arXiv subjects

Victor Gaydamachenko

Publications and source records attributed to Victor Gaydamachenko.

4 recordsLinked to original sources

arXiv2025

An rf-SQUID-based traveling-wave parametric amplifier with -84 dBm input saturation power across more than one octave bandwidth

Traveling-wave parametric amplifiers (TWPAs) have become an essential tool for the readout of quantum circuits and the search for dark matter. We report on the implementation of an rf-SQUID-based Josephson TWPA with an average saturation power of -84 dBm, while providing an average power gain of 20 dB from 3.5 to 8.5 GHz. This wide bandwidth is enabled by reducing the curvature of the dispersion in the signal band while suppressing detrimental mixing processes. With 2393 rf-SQUIDs our device has a comparable number of nonlinear elements, but achieves ten times higher saturation power than previous works, showing that using rf-SQUIDs results in a more favorable trade-off between device length and saturation power. Harnessing wideband characterization techniques we determine the TWPA's excess noise above the quantum limit to be 0.8 to 1.5 photons. In addition, we validate signal-to-noise ratio improvement as a practical measure for tuning the TWPA to minimize the total system noise, and demonstrate that its optimum does not coincide with the highest gain.

quant-ph↗

arXiv2024

Demonstration of dual Shapiro steps in small Josephson junctions

Bloch oscillations in small Josephson junctions were predicted theoretically as the quantum dual to Josephson oscillations. A significant consequence of this prediction is the emergence of quantized current steps, so-called dual Shapiro steps, when synchronizing Bloch oscillations to an external microwave signal. These steps potentially enable a fundamental standard of current $I$, defined via the frequency $f$ of the external signal and the elementary charge $e$, $I=\pm n \times 2ef$, where $n$ is a natural number. Here, we realize this fundamental relation by synchronizing the Bloch oscillations in small Al/AlO$_\mathrm{x}$/Al Josephson junctions to sinusoidal drives with frequencies varying from $1$ to $6\:\mathrm{GHz}$ and observe dual Shapiro steps up to $I\approx 3 \: \mathrm{nA}$. Inspired by today's voltage standards and to further confirm the duality relation, we investigate a pulsed drive regime, which is dual to the single flux quantum mode of Josephson oscillations, and observe a similar asymmetric pattern of dual Shapiro steps. This work confirms quantum duality effects in Josephson junctions and paves the way towards a range of applications in quantum metrology based on well-established fabrication techniques and straightforward circuit design.

cond-mat.mes-hall↗

arXiv2023

Vulnerability to Parameter Spread in Josephson Traveling-Wave Parametric Amplifiers

We analyze the effect of circuit parameter variation on the performance of Josephson traveling-wave parametric amplifiers (JTWPAs). Specifically, the JTWPA concept we investigate is using flux-biased nonhysteretic rf-SQUIDs in a transmission line configuration, which harnesses the three-wave mixing (3WM) regime. Dispersion engineering enables phasematching to achieve power gain of $\sim$20 dB, while suppressing the generation of unwanted mixing processes. Two dispersion engineering concepts using a 3WM-JTWPA circuit model, i.e., resonant phase-matching (RPM) and periodic capacitance modulation (PCM), are discussed, with results potentially also applicable to four-wave-mixing (4WM) JTWPAs. We propose suitable circuit parameter sets and evaluate amplifier performance with and without circuit parameter variance using transient circuit simulations. This approach inherently takes into account microwave reflections, unwanted mixing products, imperfect phasematching, pump depletion, etc. In the case of RPM the resonance frequency spread is critical, while PCM is much less sensitive to parameter spread. We discuss degrees of freedom to make the JTWPA circuits more tolerant to parameter spread. Finally, our analysis shows that the flux-bias point where rf-SQUIDs exhibit Kerr-free nonlinearity is close to the sweet spot regarding critical current spread.

cond-mat.supr-con↗

arXiv2022

Numerical analysis of a three-wave-mixing Josephson traveling-wave parametric amplifier with engineered dispersion loadings

The recently proposed Josephson traveling-wave parametric amplifier (JTWPA) based on a ladder transmission line consisting of radio-frequency SQUIDs and exploiting three-wave mixing (3WM), has great potential in achieving both a gain of 20 dB and a flat bandwidth of at least 4 GHz. To realize this concept in practical amplifiers we model the advanced JTWPA circuit with periodic modulation of the circuit parameters (engineered dispersion loadings), which allow the basic mixing process, i.e., $ω_s=ω_p-ω_i$, where $ω_s$, $ω_p$, and $ω_i$ are the signal, the pump, and the idler frequencies, respectively, and efficiently suppress propagation of unwanted higher tones including $ω_{2p}=2ω_p$, $ω_{p+s}=ω_p +ω_s$, $ω_{p+i} = ω_p + ω_i$, etc. The engineered dispersion loadings allow achieving sufficiently wide $3$ dB-bandwidth from $3$ GHz to $9$ GHz combined with a reasonably small ripple ($\pm2$ dB) in the gain-versus-frequency dependence.

quant-ph↗